1. Field of the Invention
This invention relates to a video signal follow-up processing system, and more particularly to an improvement of one which can take an optimal image by automatically following changes of a subject in the field of view of a video camera.
2. Description of the Related Art
As an apparatus for tracking changes of position of a subject in the field of view, there is a subject tracking apparatus in a video camera which automatically tracks the subject according to its movement. First, for a subject tracking device in a conventional video camera, an automatic subject tracking method has been disclosed in the Japanese Patent Application No. 207107/1992 filed on Jul. 10, 1992, which stores a peak value of high-frequency components of brightness signals in a measurement frame, and automatically tracks its movement as characteristics of the subject.
Secondly, an automatic subject tracking method has been disclosed in the Japanese Patent Application No. 322652/1992 filed on Nov. 7, 1992, which performs automatic tracking by forming a motion vector through matching of representative points for brightness signals of front and back fields in a measurement frame, and by assuming the motion vector as the movement of the subject.
The first automatic tracking method basically utilizes signals at peak, so that it is vulnerable to noise. Therefore the automatic tracking may not be attained in a shooting environment with low illuminance. Moreover, in principle, it extracts high-frequency components, so that the automatic tracking may not be attained for a subject with low contrast.
Furthermore, in the second automatic tracking method, it is difficult to determine whether the calculated motion vector is caused by movement of the hand on the video camera or by movement of the subject, so that a malfunction may arise in the practical use.